In many Scandinavian languages, saft is simply the word for juice, but in Sweden, “saft” has acquired a special meaning. It is used specifically to refer to a very sweet, fruity juice concentrate, which is blended with water and ice to make refreshing cool drinks. Many Swedish markets sell saft in a variety of flavors for people to mix up juices to taste, and it is also possible to make saft at home. The trend has spread to some other Scandinavian nations and communities, making saft not uncommon in many regions of the world.
The word is taken directly from the Middle High German. Incidentally, the same root word is also responsible for “zaftig,” as in “plump and curvaceous.” Use of the word can be a bit confusing, as it is generic for juice in some regions of the world, and it refers specifically to concentrates in others. If you aren't sure, you may want to ask, to ensure that you don't end up buying a bottle of fiercely sweet concentrate for a picnic when you want juice, for example.
Many safts are made with berries such as lingonberries, along with flower products such as elderflowers and rose hips. It is also possible to find fruit safts, especially citrus fruit saft like orange or lime saft. In most cases, the saft is produced by cooking the fruit so that it turns pulpy and yields its juice, and then straining the pulp to yield a rich concentrate which may be sweetened, depending on personal taste.
Many people find saft quite enjoyable, and a pleasant alternative to mixing up large pitchers of juice concentrate, as it comes in large jars which are designed to facilitate the mixing of single servings of juice. In addition to being mixed with still water, saft can be blended with sparkling water for a fizzing fruity drink, or with alcohols like champagne. Some people also mix several types of saft to create a specific flavor combination.
If you are fortunate enough to live in an area with a big Swedish community, you will probably be able to find saft in traditional flavors like lingonberry and elderflower. If you are not so lucky, you may be able to track down an import store which carries saft, and you can also order it through Swedish specialty retailers online, as well as directly from the companies which produce it.